Databases Reference
In-Depth Information
ASM DiskGroup
Used to build
ASM Disk
Used as
Grid Disk
/filesystem
Divided into
On which is built
Cell Disk
Presented as
Volume
LUN
Presented as
Presented as
Partition
Partition
Divided into
Physical Disk
Figure 25-2.
Disk organization in an Exadata Storage Cell
In Figure 25-2, the first two disks are split into two different partitions; each partition is presented to the cell
server as a LUN. One of the LUNs is used to build the root file system on the cell server where the operating system is
installed. The Exadata Storage Server (ESS) software is also installed on the file system. Since the file system has to be
on a mirrored volume for high redundancy, two such partitions are used from two different disks.
The other LUN (on the other partition of the disk) is presented to the Cell as a celldisk, The celldisk is divided
into griddisks, which are then presented to the ASM instance running on the Nodes to be used in ASM diskgroups.
So, the ASM disks are actually griddisks on Cells. Once the ASM diskgroup is created and online, the database is built
on top of that.
The disks from the cells are presented to the nodes through an Infiniband (IB) network housed inside the
Exadata rack. There are three IB switches inside a full rack for redundancy. IB offers very high throughput and very
low latency—perfect for Nodes accessing the disks on the Cells. The rack also has regular Ethernet switches—both
10 Gbps and 1 Gbps. These are used to connect to the servers from the outside. The users connect to the Nodes using
the normal Ethernet network. They can also use Infiniband to connect to the nodes, which may be beneficial for
high-throughput applications, such as reporting or ETL.
